Contemporary cut sheet handling systems have employed various sensors and processes for extracting information regarding cut sheets for monitoring machine performance and/or developing machine control responses. For instance, electrophotograhic machines sometimes sense sheet length at the supply tray output for setting inter-image erase machine controls. Sheet output sensing has also proven useful to provide jam recovery data and the like. Typically, xerographic copiers and printers include some form of paper height sensors which are often mechanically implemented.
Mechanical switches are widely used in cut sheet paper supply bins. For instance, they are used to signal that a stack of sheets in a supply bin is at an upper or lower limit. They are also used to indicate that the supply in the bin is exhausted, and this is sometimes supplemented with another switch positioned to detect that the stack is low enough that it needs replenishment by the operator.
U.S. Pat. No. 3,955,811 by David K. Gibson employs mechanical switches and a pedestal control system to maintain the stack of a standby bin in an intermediate position regardless of the amount of paper therein or its condition. U.S. Pat. No. 4,331,879 by Gersl includes a photocell assembly to monitor the top of the stack for height control.
Others have suggested using the results of stack height change sensing to warn the machine operator that an insufficient supply of cut sheets remain, or are available, in the supply bin to complete a selected machine operation. U.S. Pat. Nos. 4,503,960 by Koeleman et al and 4,535,463 by Ito et al are examples of such systems. The former bases its prediction on an assumed sheet thickness and sensed remaining stack height. Ito et al counts the number of copies run for a detected stack height change to calculate whether the remaining stack content is an adequate supply for the job.
As xerographic machines evolved, they have incorporated more and more data processing elements to control the machine functions. Further, such machines can operate more reliably if they can adjust certain operating parameters dynamically as a function of the quality and quantity of paper in the supply bin. Examples are adjustments of air pressure, picker roller force, fuser temperature and pressure operations in conjunction with staplers and stitchers and so forth. Unfortunately the known prior art does not disclose content of such machine elements based upon an accurate picture of the vital statistics and parameters of the paper in the bin. The present invention fills that void and in a manner well suited for advantageous implementation in microprocessor machine control environments.